The epidermis is a self-renewing tissue, which provides a natural barrier between the organism and the environment. Our research focuses on the dynamic process by which the epidermis maintains the proper balance between proliferation and differentiation. Combining classical genetics and modern tools of genomics, we investigate and model in mice the function of novel genes important for in utero human epidermal development. We seek to answer fundamental questions about the mechanism by which these epidermal cells produce this barrier. Specifically, how do the cells in a developing baby initially construct this wall? In an adult, how are these cells able to respond to skin wounds and build a new wall? Since the cells are not only the bricks, but also the